I don't know it exactly, but i would give 1.7.3 a try. If this will not work, try XAMPP 1.7.1 (the last release with PHP 5.2). If you found the last working version, give us a reply. I don't have a Windows 2000 machine to test it by myself
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I haven't yet done anything with it but 1.7.4 let me start Apache without the problem reported herein. I didn't try 1.7.5 because according to the dates specified at Sourceforge it is only a few days older than 1.7.7.
Some limited testing indicates that Apache seems to work (XAMPP 1.7.4 on W2K) but an attempt to start MySQL produced a problem similar to the one provoking this post.
Upon reflection, there is so much software in this package it is impossible to make any reliable determination regarding the issue of W2K inter-operation based on trial and error methods. Insofar as XAMPP advertises that it runs on W2K it would seem like Apache Friends should stop making such claims. It would also be very helpful if Apache Friends could provide a reliable statement regarding when XAMPP stopped working on W2K and possibly how to obtain a prior version that does work on W2K.